Photolithography (or lithography) is frequently used in manufacturing semiconductor integrated circuits (IC). In a typical lithography process, a resist film is spin-coated on a surface of a silicon wafer and is subsequently exposed and developed to form a pattern for etching the silicon wafer. As semiconductor fabrication technology continues to scale down where functional density has generally increased while geometry size has generally decreased, there has been a demand for a reduction in resist film thickness and a better reflectivity control during exposure. Accordingly, some new material and/or new techniques in lithography have been developed. For example, some lithography processes use silicon-containing resist over a carbon-containing bottom anti-reflective coating (BARC) layer to reduce resist film thickness. For another example, some lithography processes use a tri-layer stack that includes a resist over a silicon-containing middle layer over a carbon-containing under layer. However, these approaches present new challenges.
For example, in the tri-layer approach, the carbon-containing layer is very difficult to remove, and thus dry etch process is applied. However, when the carbon-containing layer is formed over a dielectric layer, the removal of the carbon-containing layer may damage the dielectric layer therebeneath. This unavoidably reduces device reliability.